Medieval knights (and Jon Snow from 'Game of Thrones') were famous for kneeling, which may have influenced today's marriage proposals. Here's why men get down on their knees to propose to their girlfriends .

If you're about to get proposed to and the person starts to get down on one knee, you should check to see if their shoe is off. If not, be prepared for a yes or no question.
Aside from being a reminder, kneeling to propose marriage probably has its roots in a number of long-standing historical customs—or a combination of them. As MarthaStewart.com points out, people have been kneeling (from the Latin word for “to bend the knee”) to show respect or deference for thousands of years. It may have originated in the Persian Empire, when greetings depended on social rank. The Greek historian Herodotus observed in Persia around 430 BCE that “ Where one is slightly inferior to another, a kiss is given on the cheek .” “ When the difference in rank is very great, the inferior person is forced to kneel on the ground .”

This style of greeting, known as proskynesis, was adopted by Alexander the Great when he took over the empire a century later, and some historians believe that kneeling was part of it. Many of Alexander's existing Greek and Macedonian subjects disapproved of the new ritual, believing that such gestures should be reserved for the gods, so not everyone agreed.
But the idea of kneeling as a sign of reverence has proven popular in both religious and future traditions. Catholics, for example, kneel on one knee when facing a tabernacle containing the Eucharist. And European warriors knighted after battle often knelt before their commander, who marked them with a sword.
According to Bustle, kneeling may have first taken on romantic significance during the Golden Age of Chivalry. In the 11th century, knights began forming close bonds with ladies of the court—a custom that would later be known as “courtly love.”
Since the woman was usually married, the nature of the relationship was not usually sexual, but always a serious commitment. Knights swore to serve and honor their lovers with the same zeal they would show their lords and kings. Guinevere's romance with Sir Lancelot is a classic example of courtly love, as is the story of Tristan and Isolde (although both involve adultery).
There's no clear connection between that medieval trend and today's proposal tradition, but many works of art depicting courtly love feature the man kneeling before the woman—a scene that mirrors many modern engagement photos (sans the armor).
In short, kneeling has long conveyed devotion and humility, which a boyfriend might want to demonstrate when proposing to someone forever. But if you want to propose on two feet, it doesn't violate any rules of conduct.